Two-dimensional simulation of the spin-flip in the Kapitza-Dirac effect

Many calculations in strong field quantum field theory are carried out by using a simple field geometry, often neglecting the spacial field envelope. In this article, we simulate the electron diffraction quantum dynamics of the Kapitza-Dirac effect in a Gaussian beam standing light wave. The two-dimensional simulation is computed in a relativistic framework, by solving the Dirac equation with the fast Fourier transform split operator method. Except the numerical propagation method, our results are obtained without applying approximations and demonstrate that a spin-flip in the Kapitza-Dirac effect is possible. We further discuss properties, such as the validity of a plane wave approach for the theoretical description, the influence of the longitudinal polarization component due to laser beam focusing and higher order diffraction peaks in Kapitza-Dirac scattering.